Field of the Invention
This invention relates generally to a system and method for filtering signals in a frequency band adjacent to a frequency band being employed for radio reception and, more particularly, to a system and method for filtering wireless communications service (WCS) signals broadcast in a frequency band that is adjacent to a satellite radio frequency band being received by a vehicle satellite radio.
Discussion of the Related Art
Mobile wireless cellular devices are everywhere. Cellular devices allow for the wireless transmission and reception of video, audio and data, and are relied on by users for many purposes. Those purposes and the technology, such as 4G long term evolution (LTE), to provide the services are increasing, which requires an increasing need for more wireless bandwidth and data throughput. With the explosion in demand for cellular data and voice services, there is an increasing burden on the existing frequency bands allocated for these services, where the available cellular bandwidth is becoming insufficient to meet those demands. Providing additional frequency bands for cellular services has a direct and often times measurable impact on commercial progress.
The Federal Communications Commission (FCC) regulates which frequency bands are used for what purposes in the United States. Thus, there has been significant pressure on the FCC to allocate more frequency bands for cellular services, which also provides significant revenue. In response, the FCC has recently reallocated the WCS frequency band for cellular services, where the 2305-2320 MHz frequency band is now being used for signals transmitted from mobile cellular devices to a cellular tower and the 2345-2360 MHz frequency band is now being used for signals transmitted from the cellular tower to the mobile devices.
Satellite radio, specifically Sirius and XM, have also been allocated a certain frequency band by the FCC, where Sirius satellite radio operates in the 2320-2332.50 MHz frequency band and XM satellite radio operates in the 2332.50-2345 MHz frequency band. As is apparent, the XM frequency band is contiguous and adjacent to the WCS frequency band used for signals transmitted by the cellular tower and the Sirius frequency band is contiguous and adjacent to the WCS frequency band used for signals transmitted by the mobile devices.
Satellite radios receive signals from satellites from which certain audio can be played. Those signals are at relatively low power when received by the radio. Cellular towers broadcast cellular signals to the mobile wireless devices within a certain range of the tower. Those signals are broadcast at a relatively high power from the tower to be received by the mobile devices some distance away at the appropriate data rate throughput. If a vehicle having a satellite radio is travelling within a certain proximity to a cellular tower that is broadcasting cellular signals in the WCS frequency band, those signals are received by the satellite radio antenna on the vehicle at a relatively high power, for example, possibly five magnitudes larger than the satellite radio signals being received by the antenna. For XM satellite radio signals that may be directly adjacent to the WCS signals from the cellular tower, the WCS frequency signals can overwhelm and block the satellite radio signals, where the satellite radio on the vehicle may go mute.
Also, if a vehicle having a satellite radio is travelling within a certain proximity of a mobile cellular device that is transmitting cellular signals in the WCS frequency band, where the cellular device may be in the vehicle, those signals are received by the satellite radio antenna on the vehicle and possibly at a higher power level than the satellite radio signals. For Sirius satellite radio signals that may be directly adjacent to the WCS signals from the cellular device, the WCS frequency signals can overwhelm and block the satellite radio signals, where the satellite radio on the vehicle may go mute.